This invention relates generally to bias ply pneumatic tires having a tread pattern including circumferentially extending shoulder ribs, and in particular, but not exclusively, to bias ply pneumatic truck tires having treads of the aforementioned type.
A typical bias ply pneumatic tire with a rib type tread has a pair of lateral tread edges which are formed on circumferentially extending shoulder ribs and at least one, and most commonly three, axially spaced circumferentially extending ribs located between the shoulder ribs. The ribs are spaced apart from one another by circumferentially extending grooves that are typically zig-zag in configuration, but the grooves may be straight.
The shoulder ribs of these prior art tires are subject to damage when the vehicle, to which the tires are fitted, is driven substantially parallel to a curb and caused to ride up on the edge of the curb, thereby subjecting a shoulder portion of the tire that is adjacent to the curb to a tearing action. Such damage can also occur to tires fitted on a trailer when a vehicle towing the trailer is turned in a very tight circle, or when a vehicle fitted with the tires leaves the edge of a highly crowned roadway.
The prior art solution to the problem of torn shoulder ribs has been to produce rib type bias ply tires having wide and stiff shoulder ribs to reduce the incidence of tear. This prior art solution results in a heat build up in the shoulder portions of the tire, and radially elongated cooling notches were placed into the shoulder portions of the tire to help dissipate the heat.